Question

A 20-cm long and 1.0-mm diameter thick copper wire (resistivity 1.7 × 10-8 Ωm) is connected across a 3-V battery. The current through the wire is

1-7 A.
2-125 A.
3-693 mA.
4-693 A.
5-789 A.

Answer 1

We use the ohm's law to be able to calculate things for this problem. We know that V=IR. We use this equation as follows:

now we have V=3V

R=(resistivity*length)/area of cross section of the wire
R = 1.7 × 10-8(.20) / π(0.0005)² = 4.33 x 10 -3

I = V/R = 3 / 4.33 x 10 -3 = 693 A <----- OPTION 4